Telephone system



Nov'. 11, 1941. J. N. WALTERS TELEPHONE SYSTEM 6 Sheets-Sheet 1 Filed July 5, 1940 INVENTOR J.N. WALTERS 5V 0969 61m ATTORA/EK I Nov. 11, 1941. J L R I 2,262,595

TELEPHONE SYSTEM Filed July 3, 1940 6 Sheets-Sheet 2 ga 31 kg ,9 gf g" L;

I I IIHII' INVENTOR J. N. WA LTERS ATTORA/EV Nov. 11, 1941. N, WALTERS 2,262,595

TELEPHONE SYSTEM Filed July 5, 1940 6 Sheets-Sheet 3 mn/i/vro'p J. N. WAL TERS Nov. 11, 1941. J, WALTERS 2,262,595 I TELEPHONE SYSTEM Filed July 5, 1940 6 SheetS Sh eet 4 Fla R1250 INVENTOR J.N. WALTERS A T TOR/V5 V TELEPHONE SYSTEM Filed July 3, 1940 6 Sheets-Sheet 5 lA/l/EN 7'09 J. N. WA L TE/PS awcidz A TTOR/VEV Nov. 11, 1941. J. N. WALTER TELEPHONE SYSTEM Filed July 3, 1940 n u I u n O Q u 6 Sheets-Sheet 6 INVENTOF? J. N. WA L 7' E R5 ATTORNEY Patented Nov. 11, 1941 TELEPHONE SYSTEM James N. Walters, East; Orange, N. J assignor to Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application July 3, 1940, Serial No. 343,701

Claims. (Cl. 179-27) This invention relates to telephone systems and -particularly to systems comprising an unat- It is the object of the invention to improve I the maintenance alarm equipment provided in unattended automatic oflices and in the transmission of alarms to a master ofiice.

It is usual to provide alarm apparatus in an unattended dial ofiice which is effective when a trouble condition exists to seize a trunk to a master ofilce and upon answer of the call by an operator in the master office to transmit a tone signal to indicate that the call is a trouble alarm call from the unattended oflice. It is also known to provide a trouble-checking line in the unattended ofiice with which connection may be established on a call from an operator or maintenance test man in the master oflice to determine whether any trouble exists and the character of the trouble in the unattended office. One of the trouble conditions which, if maintained for an interval of from twenty to thirty minutes, has been effective to initiate a trouble alarm call to the master office is a permanent signal condition on a subscribers line.

In ofiices in which some or all of the subscribers are provided with permanent signal lockout relays, whereby a line subjected to a permanent signal is automatically disconnected from the first selector switch and rendered ineffective to initiate another call until after the permanent signal condition is cleared, it is desirable that an alarm call be made only if there are a number of permanent signal conditions existing at th same time. This invention is an improved alarm arrangement in an unattended dial ofiice whereby an alarm call is initiated to a master ofiice when a permanent signal condition exists simultaneously on a predetermined number of subscribers lines and whereby a distinctive tone signal is transmitted to the calling operator in the master oifice on a troublechecking call if a permanent signal condition exists on said predetermined number of subscribers lines at the time the trouble-checking call is made.

A feature of the invention is a permanent signal alarm circuit comprising a marginal relay of the voltmeter type connected in parallel with a resistance through which battery is connected to subscribers line circuits and first selectors in an unattended dial oflice, the relay being operatively effective upon the occurrence of a predetermined number of permanent signal conditions to initiate an alarm call to a master ofiice.

Another feature of the invention is a permanent signal alarm circuit comprising a marginal relay of the voltmeter type for initiating an alarm call to a master ofilce upon the occurrence of a permanent signal condition on a predetermined number of subscribers lines in an unattended dial ofiice, the voltmeter relay comprising an operating winding for closing its contacts, a small permanent magnet for maintaining the contacts closed, and a reset coil which when energized opens the contacts. In accordance with this and other features, means are provided for operating the reset coil upon establishment of a trouble-checking call from the master ofiice, for transmitting a distinctive tone to the calling operator if a permanent signal condition then exists on as many as, or more than, said predetermined number of subscribers lines, and for releasing the reset coil and preventing its reoperation on the same trouble-checking call.

A telephone system embodying the features of this invention is represented schematically in the drawings which form a part of this specification. The invention is not limited to the particular system disclosed, or to systems comprising switches of any particular type but is generally applicable to any automatic switching system comprising an unattended central office and a master oflice.

Referring to the drawings:

Fig. 1 shows a subscribers station A, line LI and line circuit LCI, a line-finder switch LF! and a connector switch CI in an unattended ofiice; Fig. 1 also shows permanent signal alarm apparatus PSA in the unattended dial ofiice;

Fig. 2 shows a first selector switch SI, a connector switch C2, and a subscribers line L2 andstation B in the unattended office; Fig. 2 also shows permanent signal timing apparatus PST in the unattended dial office;

Fig. 3 shows two-way trunk circuits TCI and T02 and incoming selector switches 18! and 182 in the unattended dial office associated with interoffice trunks TI and T2 leading to a master ofiice;

Fig. 4 shows a two-way trunk circuit T03 terminating the trunk Tl at an operators position in the master oilice;

Figs. 5 and 6 show miscellaneous alarm apparatus MA, alarm sender apparatus AS, and a ringing circuit RC in the unattended dial ofiice; and

Fig, '7 shows the positional relation between provided on lines terminating in common battery central ofiices and each includes a dial or other impulse sender for controlling the operation of automatic switches through which denected from conductors 53 and I3 to efiect the sired connections are established. The line circuit LCI comprises a combined line'and cut-ofi relay I4 and a lock-out relay I6. All-of the lines in the office may be provided with a. lock-out relay but ordinarily only a part of the lines will be so arranged. If a line is not equippedwith a lock-out relay, the. lower front contact of its. line relay I4 is connected directly to sleeve.:conductor 13, the upper front contact of its relay I4: is connected directly to and through'its outer upper back contact to conductor I5, and the junction between the middle and upper windings of its relay M is connected directly to the conductor leading to the sleeve terminals in the banks of connectors such as CI. The line LI and other lines in the same group are connected .to terminals. in the banks of a group of line-finder switches. including the line finder LFI and a start relay Iiiv common to these lines is provided for starting an idle line finder in operation re.- sponsive to the origination of a call over any line in the group. The line finder LFI is represented in the drawings by a set of brushes 4|, 42 and 43 and a single set of terminals. Reference may be had to the patent to R. L. Stokely No. 1,799,654, April 7, 1931, and to the patent to T. L. Dimond No. 2,210,068, granted Aug. 6,1940, for a description of the operation of such line-finder switches.

Each of the line finders is permanently asso- 5 ciated with a first selector switch, theline finder LFI. being connected to theselector SI. The selectors may have direct access to groups of outgoing trunks. and. to connector switches as. shown in the drawings. If, however, the number of sub.- scribers in the office makesnecessary the pro.- vision of one or more additional stages of selection, intermediate selectors will be provided.

The selector SI comprises a set of brushes 6'1,

6.8 and 69 and a bank of terminals-which is represented in the drawings by one set of terminals 10 in a level giving access to connector switches and two sets of terminalsv BI and 82 in a'level givingv access to a groupof. trunks to the master The selector SI further comprises a. line ofiice. relay 55, a release relay 56, a change-over relay 51, a switching relay 58, a rotary-stepping relay 59, a vertical-stepping. magnet 6.1, a rotary-step- .ping magnet 62, a, release magnet 63, a set of vertical oil-normal springs 64 and eleventh rotary-step springs 65, all of which have usual and well-known functions. The selector SI also com.- prisesa release-control relay 60. which controls the connection of holding ground potential to and through conductor 53, tov the associated line finder LFI. .After connection of a calling line to selector SI, the line relay 55. and release relay 5.6 are. actuated. to connect. holding ground p0..- tentialto conductors 53 and I3, When the calling subscriber dials. the first digit: of a called subscribers number, the selector SI is operated to extend the connection to the next switch or to a trunk; and in this case relay performs no useful function. But, if the calling subscriber fails to dial, or if the extension of a link to selector SI is due to a trouble condition, relay 60 is operated to place the holding ground potential under control of the permanent signal timing apparatus PST; and, if the selector SI has not been selectively operated by dial impulses within an interval of two minutes after relay 6Ilis operated, the holding ground potential is discon- For this reason the release relay 56 and release relays of the other first selectors are connected through the windings of relays such as relay I 2| of the miscellaneous alarm apparatus MA to battery in the permanent signal alarm apparatus PSA in order that the permanent signal alarm relay I37 of the miscellaneous alarm apparatus will be responsive to permanent signal conditions on all lines, as hereinafter explained in detail.

Groups of connector switches have access to subscribers lines for completing calls thereto, the connector CI being one of a group having. access to the line LI and the connector CZ being one of a group. having access to the line L2. The connectors are multipled to terminals in the banks of local selectors (first selectors such as SI or intermediate selectors if provided) and to terminals in the banks of incoming selectors such as IS! and 152-. The connector CI is. represented by a set of brushes and a single set of terminals, and the connector C2 by a set of brushes "Ii, 72 and 73, and. two sets of terminals I4 and 15., the

magnets, relays and other associated apparatus being omitted.

The trunks TI and T2 represent a group. of two-way trunks between. the unattended ofilce and an operators position. in the master office. The trunks TI and T2; terminate in two-way t unk c cu ts TC and T02 in. the unattended ofiice and in two-way trunk circuits such as IC3 in the master oil-ice, of which only the trunk circuits TCI and T03 are shown in detail. trunk circuits TCI and T02 are connected to terminals 8| and 82 in. the bank of selector SI and in like. manner to other selectors in the unattended oflice, thereby enabling. seizure of the trunks on calls outgoing to the -master ofiice. The trunk circuits TCI and T62. are also connected to incoming selectors IS! and 1S2. which have access to the groups of connectors in the unattended office, the. incoming selectors, being operated on incoming calls under control of the calling operator in the master ofiice to select idle connectors in groups. having access to the called lines. Each of thetrunk circuits TCI and T02 is also connected to the alarm sender apparatus shown in Fig. 6 so that the one or the other of these trunks. may be seized when a trouble condition occurs in the unattended ofiice and thereby transmit to the operator in the master ofiice an indication of trouble as hereinafter explained in detail. Each of the incoming selectors ISI and IS? isrepresented in the drawing by a set of brushes and-a single set of ter- The responsive to seizure on outgoing calls, a line relay 2I3 and switching relay 209 responsive to seizure on incoming calls, a polarized supervisory relay 2 I4 responsive to answer of the called subscriber on incoming calls, a reversing relay 2I2 controlled by relays 2H and 2I4 responsive to seizure on outgoing calls and to answer of the called subscriber on incoming calls, and a relay 201 for establishing a non-inductive impulse, repeating bridge during the repeating of impulses to the incoming selector ISI and a connector switch on incoming calls. The trunk circuit TC2 is similar to the trunk circuit TCI The trunk circuit TC3 comprises a jack J3, a repeating coil RC3, a polarized relay I responsive to seizure of trunk TI in the unattended office, relays 252, 254 and 255 for controlling the answering lamp 253, the busy lamp 251 and the connection of a busy potential to the sleeve of jack J3, a sleeve relay 251 and an auxiliary sleeve relay 258, a cut-through relay 26I, and a group of relays 262, 263, 264 and 265 which operate to establish the dialing condition on a call from the master oflice to the unattended oifice.

The cord CD and operators position equipment at which the jack J3 is located may be similar to cord and position equipment disclosed in detail in the patent to R. E. King, et al., No. 2,208,165, granted July 23, 1940.

The permanent signal alarm apparatus PSA shown in Fig. 1 comprises a voltmeter relay the operating winding 3I of which is connected in parallel with resistors 23, 24 and 25 to supply battery to the locking windings of the look-out relays I6 of subscribers line circuits which are arranged for lock-out and in parallel with resistor 24 to supply battery through the windings of relays such as relay I2I in the alarm apparatus MA to the windings of the release relays of the first selectors, for instance release relay 56 of selector SI. The terminals 21 enable the connection of a desired number of resistors 26 in circuit so that the voltage required for operating the voltmeter relay 30 may be adjusted to secure its operation when a permanent signal condition exists on a desired and predetermined number of lines of either type, that is lines equipped and lines not equipped with lock-out relays. The resistances 23 and 24 are so chosen that the increase of current through the winding 3| of voltmeter relay 30 due to the operation of a permanent signal lock-out relay I6 is equal to the increase therethrough due to seizure of a selector SI and closure of the circuit through the winding of its release relay. The operation of relay 30 causes the successive operation of relays 33, 34 and 35. The operation of relay 35 lights lamp 36 and effects the operation of relay I31 of the miscellaneous alarm apparatus MA to initiate an alarm call to the master ofiice as hereinafter described. The stationary contact of the voltmeter relay comprises a small permanent magnet and the movable contact spring has a small iron tip so that'the contacts are held closed, after relay 33 opens the circuit through coil 3I, until restored to normal by the energization of a reset coil 32. Reference may be had to the patent to A. H. Lamb, No. 2,014,385 granted September 11, 1935 for disclosure of a relay of this type. Ihe reset coil 32 is operatively controlled by relay I55 of the miscellaneous alarm apparatus to effect the release of relays 33, 34 and 35 when relay I55 operates due to seizure of the terminals 15 by a connector C2 on a trouble-checking call from the master office as hereinafter described. The permanent signal alarm apparatus further comprises a'relay 48 for disconnecting the reset coil .32 and holding it disconnected as long as the trouble-checking call is maintained by the operator.

The permanent signal timing apparatus PST comprises two sets of relays, one set comprising relays I06, I01 and I08 for completing a timing cycle of operations in two minutes and the other comprising relays H6, H1 and H8 for completing a timing cycle in twenty minutes. Upon connection of ground to start conductor I09, relays I06, I01 and I08 are successively operated and then successively released in a two-minute cycle, ground being disconnected from conductor IOI when relay I86 operates and reconnected to conductor IOI when relay I08 releases, ground being disconnected from conductor I02 and connected to conductor III] when relay I08 operates and reconnected to conductor I02 and disconnected from conductor IIII when relay I08 releases. Upon release of relay I08 at the end of a two-minute cycle, ground is connected to conductor IOI to operate the release-control relay 60 of all first selectors which have been seized during the preceding two-minute interval and which have not been selectively operated by dial impulses to select a desired group and seize an idle trunk in the selected group; and ground is connected to conductor I02 to hold the line finders associated with these first selectors. When relay I08 next operates at the end of another twominute interval, it disconnects the holding ground potential from conductor I02 to cause the release of the line finders and operation of the look-out relays of lines associated with first selectors whose release-control relays 60 were operated at the beginning of, the interval and which have not been released because group selection and seizure of a trunk has not been completed. Upon connection of ground to start conductor H9, relays II6, H1 and H8 are successively operated and then successively released in a twenty-minute cycle, ground being disconnected from conductor III when relay II6 operates and reconnected to conductor III when relay II8 releases, and ground being connected to and disconnected from conductor I20 by the-operation and release of relay I I8.

The miscellaneous alarm apparatus MA comprises relays such as relay I2I through the windings of which battery is connected to the release relays of first selectors, relays such as relay I3I through the windings of which battery is connected to the release magnets of selectors and connectors, fuse alarm relays such as relay I44, permanent signal alarm relays I24 and I31 and a trouble-checking-call relay I55. The miscellaneous alarm apparatus also includes other relays and apparatus necessary for the operation of visual and audible alarms and for initiating the operation of the alarm sender AS as hereinafter described.

The alarm sender AS comprises relays I and I86 individual to trunk TI and relays I and I96 individual to trunk T2, relays I1I, I12 and I13 responsive to alarm conditions for effecting seizure of the one or the other of trunks TI or T2 if idle, a transformer I10 for impressing a trouble tone across the seized trunk, a relay I14 operativ-ely responsive to the answer of a trouble call over either of trunks TI or T2, and a relay I16 for preventing a second seizure of one of these trunks if the alarm condition continues after a trouble call is answered.

The ringing circuit .RC, represented :by a 'rectangul'ar enclosure in Fig. 5, is similar to that disclosed in the patent to J. M. Duguid et Sal. No. 2,225,907 granted Dec. 24, 1940. It comprises a motor start relay MS, tone transformers LTI and LT2, and code I and code 2 ringing sources which together with the aforementioned transformers supply the tones for indicating various alarm conditions on trouble-checking calls from the master ofiice.

Assume now that a call is originated at station A, Lthereby closing a circuit from battery through the middle and upper windings and a back contact of line relay I4, "conductor I 2, over one of the conductors of line LI and through the telephone at station A, back over the other conductor. of line L-I, conductor II, through a lower back contact and the lower winding of relay I4 to ground. Relay I4 is thereby'partially energized to close its upper and inner lower front contacts without affecting any of the other contacts. At the upper front contact of relay 14a circuit is closed for operating the start trel ay 1 0. The operation of relay I10 causes the startingLof an idle line finder LFI in the manner described in the aforementioned patent to T. L. Dimond. When thebrushes M, 42 and 43 of the line :finder LFI find the terminals of the line LI, ground momentarily supplied in the line-finder circuit :is connected through brush 43, conductor .13, a back contact of relay If6, lowermost front contact of relay I4, another back contact of relay I6, and through the middle winding o'fre'lay I 4 to battery.

- Relay :I4 is thereby energized .to operate all of its contacts, disconnecting the conductors of line LI from the windings of .relay I4 and opening the operating circuit of start relay I 0. The line LI is connected through con'd ctors I 'I and IE2, brushes '4I and 42 of line fi er LFI, conductors and 52, and through back contacts of relay 58 to the windings of line relay 55 of selector SI, the upper winding of relay 55'being connected directly to battery and the lower winding of :relay 55 being connected through normally closed :con-

tactsof eleventh rotary-step springs 65 and conductor I03 to ground through the right winding of dial tone transformer I36 in the miscellaneous alarm apparatus MA.- Relay 55 .is thereby operated, closing a circuit for operating release relay 56 in series with relay I2I of the rmiscellaneous alarm apparatus MA. Relay .56 connects ground to conductor 53 to hold relay I4 operated and connects the upper winding of relay "60 to conductor I'IlI leading to the permanent signal timing apparatus. .If relays I05 and I108 are then normal, or if these relays both become :normal before selection of a level and an unguarded set of terminals therein is completed, relay 6'0 operates, closes a locking circuit through its lower winding, and transfers the test conductor 53.from ground at the front contact of relay 56, through conductor I52, to groundat a back contact of :timing relay I 98.

The operation of relay I 2| of the-miscellaneous alarm apparatus causes the successive operation of relays 42-2 and I23. Relay :I23connec'ts ground to the start conductor 459 leading .to the ringing circuit RC and connects ground to start conductor I09 leading to the permanent signal timing apparatus .PST to start the operation of timing relays I EH5, HM and I58 if not already in operation. Relay I2-I also closes a circuit for energizing the left, primary winding of dial tone transformer I 35 :in series with the slow tone source L'I2 of the ringing circuit, the right winding of transformer I 38 being thereby rendered effective to transmit dial tone through conductor I03 to selector SI and other first selectors and theassociated calling subscribers awaiting dial tone. The operation of relay I2I further causes the successive operation of relays I24 and I26, thereby connecting ground to start conductor H 9 to start the operation of :timingrelays H6, H1 and H8. If relays I2 I, I24 and 126 are held operated, due to 'a trouble condition for an interval during which timing relays I I6, H1 "and H8 complete a timing cycle, the connection of ground to conductor III causes theaoperation 0f relay'IZI. Relay I2.I locks under control of relay I25, and at the end of the cycle the connection of ground to conductor 120 causes the operation of relay I28. Relay I28 flocks under control of relay -I26, disconnects ground from start conductor H9, and connects the code I iringingconductor through condenser I30, a front contact of relay I28 and back'contacts of relays I48, I31 and-I4'5-to a front contact of the trouble-checking-call relay I55, so

that if relay I155 operates ashereinafter described on a call from an operator in the master office, a distinctive trouble tone will-be transmitted to the operator;

Assume now that the calling subscriber dials the .first digit of the called subscribers number before relay operates or, if relay tfivhas operated, before the next operation of timing relay I98. Relay releases and reopera'tes in response to each impulseof the series created by the dialing of this digit. Being :slow in releasing, relay 56 remains operated While these impulses are being received. The release "of relay 55 in response to the first impulse closes a circuit for operating the vertical-stepping magnet BI and the change-over relay 57 in series. The operation of magnet *5! steps the brushes El, 68 and 69 up to the first level *of the terminal 'banlc, As soon-as the shaft moves out :of its normal position the vertical off-"normal springs 64 are actuated thereby closing a circuit including the front contact of relay 5'! for operating relay 59. Relay 59 locks under the control of the rotary-stepping magnet 62 to ground at a back contact of relay 58. When relay 5'5 reoperates at theend of the first impulse, magnet -6I releases; but relay 5'I'is slow in releasing and remains operated until all of the impulses in the series have been received by relay 55. Each succeeding release and reoperation of relay -55 causesthe reoperation-and re lease of magnet 54, thereby advancing the brushes of the switch to the level corresponding to the digit dialed. When relay 57 releases after the last impulse -of the series has been received, the rotary-stepping magnet 62 is operated to advance the brushes into engagement with the first set of terminals in the selected level. The'operation of magnet 52 also causes the release :of relay 59; and the release of relay'59 causes the release of magnet 62. The release of magnet -62 closes a busy test circuit from battery, through the winding of relay 59, upper contact of springs 64, back contact of magnet '62, lower contact of the eleventh rotary-step springs 65, a back contact of relay .58 and the test wiper '69 to determine whether the trunk or the switch connected to the first set of terminals in the selected level'is busy or idle. If this trunk or switch is busy, ground potential connected to the terminal engaged by test wiper #69 causes the reoperation of relay 59; and in this case relay 59 again closes the circuit for operating magnet 62 to cause the advance of "the brushes to thenext set of ter-,

minals in the level. Relay 59 and magnet 62 repeat their cycle of operations to cause advance of the brushes from one set of terminals to the next until an unguarded set of terminals is encountered. If the brushes reach the eleventh rotary position without finding an idle set of terminals, the springs 65 are actuated to prevent further operation of relay 59 and magnet 62 and to connect the lower winding of relay 55 through conductors I04 and I51 to the tone transformer LTI in they ringing circuit RC. An all-trunks-busy tone is thereby transmitted to the calling subscriber. If and when the test brush 69 engages the test terminal of an idle trunk or switch, there being no guarding ground connected thereto to cause the reoperation of relay 59, relay 58 is operated by the current in a circuit from battery through the winding of relay 59, upper contact of springs 64, back contact of magnet 52, lower contact of springs 65, winding of relay 58, to ground at a front contact of relay 56. Relay 59 is marginal and does not reoperate in series with relay 58. Relay 58 disconnects the calling line from the windings of relay 55 and extends the connection from the calling line to the selected trunk or switch by connecting conductors 5I and 52 to the brushes 6'! and 68. Relay 58 also connects ground to the test brush B9 to guard the selected trunk or switch against seizure by another selector prior to the connection of busy ground to the test terminal by the seized trunk or switch in the usual manner. When relay 55 releases, it opens the circuit energizing relay 56, but relay 56 is slow in releasing and does not release until a busy and holding ground potential has been connected to the terminal engaged by brush 69 to hold relay 58 operated. When relay 56 releases, it causes the release of relay 60, if operated. With relay 60 normal, conductor 53 is connected, through a front contact of relay 58, A

to the test brush 69 so that the busy, ground potential connected to the terminal engaged by this brush is also effective to hold the line finder LFI and to hold the combined line and cut-off relay I4.

Assuming that the called subscriber is in the unattended office, the impulses created by the dialing of the remaining digits of the called subscribers number effect the operation of addi-, tional selectors, if any, and a connector C2 to establish a connection with the called line in usual and well-known manner. If the called line is idle a ringing circuit is closed; and when the call is answered the ringing circuit is opened, the talking circuit is established and the connection is maintained under the control of the calling subscriber in usual manner. When the calling subscriber restores the receiver to normal, holding ground potential is disconnected in usual manner from the terminal engaged by brush 69, causing the release of relay 58 of selector SI, the release of the line finder LFI and the release of the combined line and cut-off relay I4. When relay 5B releases, it closes a circuit from ground at its inner lower back contact through back contacts of relays 55 and 56, the lower contact of springs 64, winding of release magnet 63, conductor I05, upper winding of relay I3I in the miscellaneous alarm apparatus, through fuse I to battery. The operation of magnet 63 causes the shaft and brushes of selector S! to be restored to normal. When the shaft reaches normal, the springs 54 are restored to normal, thereby opening the circuit through release magnet 63 and relay I3I.

If, however, the selector iii . contact of relay shaft fails to return to normal after relay 58 releases, the'continued operation of relay I3I causes me successive operation of relays I33 and I34 and the lighting of lamp I32 of the miscellaneous alarm apparatus. At its upper front contact, re-

ground is next connected to conductor, IIO, the

uppenwinding of relay, I48 is-operatively energized and' locked under control of relay I34. At its lower back 'contactjirelay I48 disconnects ground fromconductor I09 and at itslower front contact closes a circuit for lighting lamp I46 and operating the alarm control relay I41. Relay I41 closes the circuit for operating the audible alarm I50. With relay I48 operated, tone conductor I51 is connected through condenser I49, a front I48 and back contacts of relays I31 and I to a front contact of the troublechecking-call relay I55, so that if relay I55 operatesas hereinafter described on a call from an operator inthe master ofiice, a distinctive trouble tone will be transmitted to the operator.

Assume next that, the selector SI is selectively operated by the first digit dialed at station A to select the group of trunks leading to the master ofiice, that the trunk TI is idle and that the switching relay 58 is operated when the brushes 6?, 68 and 09 engage the first set of terminals 8| in the group. When relay 58 operates, it extends the connection from the'calling line LI to and through brushes 01, 68 and 69 ,tothe trunk circuit TCI, thus completing a circuit for operating the line relay 2I I. This circuit is traced from battery through-the, right winding of relay 2! I, a back contact of relay 209, upperleft winding of repeating coil RC;I, another back contact of relay 209, conductor 202, brush seer selector SI, front contact of relay 58, conductor 52, brush 42 of line finder LFI, conductor I2, over one-of the conductors of line LI,--through the telephone of station A, back over the other conductor of line LI, conductor II, brush '4I, conductor 5|, front contact of relay 58 of selector SI, brush Bl, conductor20l, a back contact of relay 209, lower left winding of repeating coil RCI, another back contact of relay 209, through the left winding of relay 2II to ground. Relay 2 closes circuitsfor operating relays 205 and 2I2. Relay 205 connects ground'to test conductor 203 to hold the switching relay 58 of selector SI after relay releases, and to guard the trunk circuit TCI against seizure by any other seletcor having access thereto. This ground is further extended from conductor 203 through conductor I 83 in the alarm senderapparatus' to operate relay 1252.

, guish lamp-253.

c'uit ior relay 254 and completes a talking conofiice, thereby effecting the operative energizae tion of both windings of the, polarized; relay 251 of trunk circuit TC4. Although the; windings of relays 2l3'and 25! are normally connectedin a. closedcircuit over" trunk T!., the current in this circuitis not strong'enough to operate the marginal relay 2|3 and is in the non-operating direction with respect to relay 25!. The, operation of relay 25! closes a circuit for operating Relay 252' closes a circuit for lighting, the answering lamp 253 and a circuitfor operating'jfrelay 25 4. Relayt254 closes a circuit: for operating relay 255'. Relay 255 closes a circuit for lighting busy lamp 25'! and connects a busy potential through resistor 256 and the lower winding of relay 251170 the sleeve of jack J 3.

When an operator answers the call by inserting the plugP! of a cord CD in jack J3, a circuit isclosed from battery in the operators position circuit through the sleeve-conductors of plug P! and jack J3; and the upper high resistance winding-of relay 251" to ground. Relay 25! operates, closing a circuit for operating relay 258. Relay 258 closes a circuit for operating relay 25! Q closes a short circuitaroundtheupper, high resistance winding of relay 25!, thereby causing the operation of relay 2!3 of trunk circuit TC!, and opens the circuit through the winding of relay 252 to release this relay and thus extin- Relay' 26! closes a holding cirnec-tion between the right windings of repeating coil RC3 and the line conductorsof jack J 3. v j The aforementioned operation of marginal relay ;2! 3 when the call is answered, closes a circuit foroperat'ing relay 204. Relay 204 disconnects condenser 206- from conductor 20! to e'nd'=the-transmission of ringing tone to the callingsubscriber; disconnects ground'from the start conductor J59 of the ringing circuit RC, and closes" a circuit'for holding relay 205. The talking connection between the callingline and the opera-torin'the master oilice includes the repeatingcoils RCI- and RC2 and the conection is under the joint control of thecalling subscriber and the answering operator. When the calling subscriber releases the connection, relay 2!! re-- leases; 'The release of relay 2| causes the release of relay 2;!2, thereby restoring the current over trunk-T2 to its normal direction to efiect the release of relay 25! over trunkcircuit T03 in,

the master ofiice. After relay 2!! releases, relay 205 is held under the control of relays H3 and 204. When relay 25! releases,'it connects ground to thelow resistance winding of relay' 25'! thereby causingthe lighting of a supervisory lamp in the operators cord circuit as a disconnect signal. When the plug, P! of cord CDi's disconnected from jack J3, relay 25'! releases, causing the successive release of relays 258 and 26!; Relay 252 reoperates if relay 25! v has, not yetfreleased. The. release'of relay 258 opens the short circuit around the upper high 5 resistance winding of. relay 25!, thereby causing f the release ofrelay 2!3-. of trunli circuit TCI. The release of both relays 2!! and 2!3 in trunk circuitTCh causes the. release of relays 204 and a 205.

1 fromconductor-203 to, efiect the release of relay Relay 205 disconnects. ground potential 186. in the alarm sender AS; the release of relay 5 50 of selector 'S!,.the release of relay I4 of line j circuit LC!, and the return of the line-finder switch LE! to normal in the usual manner. The I release-f relay 58 causes the return of the shaft .of repeating coil RC3 and 262 operate.

and brushes of selector 8! to normalas hereinbefore described.

Assume next that an operator in the master officeinserts the plug of'a cord in jack J3 to initiate a call to a subscriber at an unattended ofiice. Relay 25? operates in the circuit including the sleeve conductors of jack J3 and plus P! to battery in the operators position circuit. Relay 251 closes a-circuit for operating relay 258. Relay 258 closes a short circuit around the upper winding of relay 25.! to effect the, operation of relay 2 !3 of trunk circuit TC!-, closes a circuit for operating relay 26!, and connects ground to the lower winding of relay 25'! to effect the lighting of a supervisory lamp in the cord circuit CD. Relay 26! closes a circuit for operating relay 254, connects the windingof relay 254, through the upper right winding to the tip of jack J3 and connects ground at the outer lower front contact of relay 258 through resistor 265, inner back contact of relay 204, inner upper front contact of relay26l, lower right winding of repeating coil RC3 to the ring conductor of jack J3. Relay 254 closes a circuit for operating relay 255. Relay 255 lights the busy lamp 251; The operation of relay 2!3 of trunk circuit TC! closes a circuit including back contacts of relays 205 and H2, through the winding of relay 209. Relay 209 operates, thereby connecting its winding to sleeve conductor 233 of the. associated incoming selector IS! and extending ground potential to conductor 203' to mark the trunk circuit TC! as busy in the banks of selectors having access thereto. Relay 209 closes a bridge comprising the winding of relay 2 i4 and resistor 2 5, in parallel, across conductors 23! and 232- of selector IS! to prepare this selector for operation by dial impulses. The selector 1S1! connects a holding ground potential to-sleeve conductor 233 in, the usual manner to hold relay 209.

When the calling operator operates the position dial key, battery is connected through the tip conductors of plug P! and jack J 3-, a front contact of relay 26!, upper right winding of repeating coil nect battery through thering conductor of plug P! to the ring conductor of jack J3, relays 263 Relay 262 looks under controlof, relays 254. and 258, and opens the circuit through the winding of relay 26!. Relay 26! releases, disconnecting the ring conductor of jack J3 from condenser 250. Relay 26! connects ground to the winding of relay 253, thereby short circuiting the upper winding of relay 202 to prepare relay 263 for response to dial impulses. With relays 263 and 262 operated, the bridge comprising the lower winding of relay 25! is disconnected from trunk T! and the impulse repeating contacts of relay 263 are connected across the conductors 22! and 222. When the operator dials the number of a called subscriber, relay 263 is alternately released and reoperated responsive to dial impulses. by the contacts of relay 203 over trunk T2 to relay 2l3 of trunk circuit TCI. When dialing is completed, the restoring of the operators dial key:

tip of the cord, re-

disconnects battery from the leasing relay 264. Relay 254 opens the connection Corresponding impulses are transmitted.

between repeating coil RC3 and the tip of jack J3, short-circuits the contacts of relay 263 and releases relays 265 and 262. The release of relay 265 disconnects the winding of relay 263 from the ring of conductor of jack J3 and opens the holding circuit of relay 254. The release of relay 262 disconnects the contacts of relay 263 from trunk TI and reestablishes the bridge comprising the lower winding of relay 25! across conductors 22! and 222. The release of relay 262 also causes the reoperation of relay 26! and completion of the talking connection between jack J3 and repeating coil RC3. Relay 26! recloses the operating circuit of relay 254 and relay 254 reoperates. Since relay 255 is slow in releasing,it remains operated during the transfer from dialing to talking conditions.

Relay 2 I3 of trunk circuit TC! is alternately released and reoperated by the dialing impulses transmitted over conductors 22! and 222 by the contacts of relay 263. When relay 2I3 releases in response to the first impulse of the train, it opens the bridge across conductors 23! and 232 and closes a circuit including a back contact of relay 2 I2 and a front contact of relay 269 for operating the slow-*to-release relay 201. With relay 201 operated, the reoperation of relay 2I3 closes a bridge comprising resistor 208 across conductors 23! and 232 in place of the bridge comprising the winding of relay 2! 4. Relay 201 remains operated while each train of impulses is being repeated by relay 2I3. The release of relay 201 after each train of impulses, reconnects the winding of relay 2!4 across conductors 23! and 232 for receiving supervisory signals.

The first train of impulses repeated by relays 253 and 2I3 controls the operation of the incoming selector IS! to select a corresponding group of trunks. This selector thereupon operates automatically to select an idle trunk in the selected group, which trunk leads to a connector C2 or to an intermediate selector if such selectors are provided. The impulses created by the dialing of the last two digits of the called subscribers number are repeated by relays 263 and 2I3 to control the operation of a connector C2 to complete connection with the called line in the usual manner. If the line is idle, the called station is signaled. If the call is answered, the connector functions in a well-known, manner to reverse the direction of current through conductors 23! and 232 to operate relay 2!4. Relay 2!4 closes a circuit for operating relay 292; and relay 2I2 effects the reversal of current through conductors 22! and 222 to operate relay 25! of trunk circuit TC3. The operation of relay 25! disconnects ground from the lower winding of relay 251 to extinguish the supervisory lamp in the operators cord circuit. The talking connection between the operator and the called sub scriber includes the repeating coils RC! and RC3 and is under-the sole control of the operator.

If the called subscriber restores the telephone to normal before the operator disconnects, the

connector 02 restores the direction of the current through conductors 23! and 232 to successively release relays 2!4, 2l2 and 25! and thus cause the lighting of the supervisory lamp in the operator's cord circuit. When the operator disconnects, relays 251, 258, 26!, 254 and 255 are released. The release of relay 25B opens the short circuits around the upper winding of relay 25!, thereby causing the release of marginal relay 2I3 in trunk circuit TCI. The release of relay 2I3 opens the operating circuit of relay 263 and opens the bridge across conductors 23! and 232, thereby causing the release of the incoming selector IS! and the connector C2. If at that time the called subscriber has failed to hang up, the connector switch is held operated but the incoming selector IS! is restored to normal in usual manner. When the called subscriber hangs up, the connector switch is also restored to normal in usual and well-known manner.

Assume next that the selector S! has not been selectively operated by dial impulses to select a group and a set of terminals therein by the time that ground is next disconnected from conductor I 62 following the operation of relay 60. In this case the disconnection of ground from conductors I02 and 53 effects the return of line finder LP! to normal, thereby causing the release of relays 55, 56 and 66. The disconnection of ground from conductors I02 and 53 also effects the operative energization of the upper winding of the permanent signal lock-cut relay It in series with the middle winding of relay I4.- Relay I6 is thereby energized sufficiently to close its inner lower front contact and energize its lower winding to complete the actuation of its contacts. Relay I4 is not held operated by its middle winding in series with the upper winding of relay I6 but is slow in releasing so as to insure the operative energization of the lower winding of relay I6. When relay I4 releases, it opens the holding circuit of relay I6 and again closes the circuit through its three windings in series with the conductors of line LI. If the permanent signal condition has not been cleared, relay I4 immediately reoperates partially so as to again close the holding circuit of slow-to-release relay I6 before this relay releases. With relay I6 operated, the partial energization of relay I4 is ineffective to cause the operation of start relay I0 and no line finder is started in search for the line. l/vhile relay I6 is operated, ground potential is connected through lamp I1 and conductor I8 to operate relay I24 of the miscellaneous alarm circuit. If not previously operated, relay I24 causes the operation of relays I26, I21 and I28 under the control of timing relays IIB, II1 and II8 as hereinbefcre described to establish the desired trouble tone condition for a troublechecking call in case such a call is originated by the operator in the'master ofiice, while the trouble condition exists.

Whenever thereis a large enough number of permanent signal conditions existing at one time to cause the operation of the voltmeter relay 36 and the condition continues long enough to cause the successive operation of relays 33, 34 and 35 of the permanent signal alarm circuit PSA, relay I31 of the miscellaneous alarm circuit MA is operated. Relay I31 connects the tone source LT2, through condenser I38 and the back contact of relay I45, to the front contact of troublechecking call relay I55; so that, if this relay operates due to seizure of the trouble-checking terminals 15 on a call from the operator in the master ofiice, a distinctive tone will be transmitted to the operator. Relay I31 also closes a circuit for operating relay I1! of the alarm sender apparatus AS to initiate a trouble call to the master ofiice as hereinafter described.

If a fuse alarm relay I44 of the miscellaneous alarm circuit is operated, due to the operation of a fuse, such as fuse 26 or fuse I46, an aisle pilot lamp such as I43 or I53 is energized. Relay !44 closes a circuit for lighting lamp I46 and operating relay I41; and relay I41 controls the audible alarm I50. The operation of relay I44 also causes the operation of relays I45 and I46. Relay I45 connects ground to conductor I6I to operate relay I12 of the alarm sender AS; to initiate a trouble call to the master ofiice. Relay I48 connects tone conductor I51 through, cone denser I49 to the front contact of relay I55 so that the desired trouble tone will be, transmitted to the master office operator if relay I55 operates due to seizure of terminals on a troublechecking call.

' attended oflice.

relays I86 and I96, relay I86 being normal if trunk TI is idle and relay I96 being normal if trunk T2 is idle. Whichever of relays I85 and I95 operates first, it looks and opens the circuit for operating the other. If relay I85 operates, it connects the secondary winding of transformer I10 across conductors I8I and I82 and connects supervisory relay I14, through conductors I 18 and I84, in parallel with relay 204 of trunk circuit TCI. If relay I95 operates, it connects the transformer I10 across conductors I BI and I92 and connects supervisory relay I14, through conductors I18 and I94, in parallel with the relay of trunk circuit TCZ which corresponds to relay 204 of trunk circuit TCI.

Assuming that the operation of relay I13 causes the operation of relay I85, the connection of the right. winding of transformer I10 across conductors I8I and I82 causes the successive operation of relays 2H and 2I2 of trunk circuit TCI. Relay 2I2 reverses the current over trunk TI to operaterelay I of trunk circuit TC3. Relay 25I causes the successive operation of relays 252, 254 and 255, and the lighting of lamps 253 and 251. When the call is answered, relays 251, 258 and 26I operate, relay 252 releases and lamp 253 is extinguished. Relays 254 and 255 are held under the control of relay 26!. The

operation of relay 258 short-circuits the upper winding of relay 25I, causing the operation of relay 2I3 of trunk circuit TCI. Relay 2I3 closes acircuit for operating relay 284 and closes a circuit through conductor I84 for operating relay I 14 of the alarm sender apparatus. Relay 204 closes a circuit for holding relay 205. Relay I14 locks under control of relay I1I or relay I12, dependingupon which of these relays operated to initiate the alarm call. The operation of relay I 14 also closes a circuit from ground through the left winding of transformer I10, conductor I19, a front contact of relay I14, a back contact of relay I16, conductor I63, to tone conductor I 51 thereby transmitting a tone to the answering operator to indicate that the call is a trouble alarm call. When the operator releases the connection, relays 251, 258 and 25I release. Relay 258 opens the short circuit around the upper winding of relay 25I to release relay 2I3 of trunk circuit TCI. The release of relay 2I3 causes the release of relay 204 and disconnects ground from conductor I84, thereby opening a. short circuit around the winding of relay I16 of the alarm sender apparatus to cause its operation in parand 20.5 of trunk circuit TCI so that this trunk may now be seized on another call. Relays I14 and I16 remain operated as long as; either of relays IN or I12 is operated. When the trouble conditions; clears, and all of relays such as I 31 and; I45 in the miscellaneous alarm circuit are normal, relays I1I, I12 and I13 are released and relays I14 and I16 release, thereby restoring the alarm; senderapparatus to. normal.

Assume now that an operator in the master;- oflice initiates a trouble-checking call to the un- Upon connection of a cord: CD withjack J 3,. trunk circuits T03 and TCI operate as hereinbefore described to prepare the incom-. ing selector ISI for response to the impulses created by the dialing of the first digit of the.

trouble-checking number. The. selector ISI is selectively controlled by these impulses to select; a connector C2, and the connector 02 is selectively operated responsive to the. impulses created by the dialing of the last two digits of the number to select the trouble-checking line terminals 15. Upon seizure of these terminals,'relay I of the miscellaneous alarm apparatus MA is operatively energized in a circuit from battery through its winding, conductor 19, through the test terminal and: test brush 13' of the connector C2 to ground. The two-element gas-filled tube I56, bridged across conductors 11 and 18, responds to ringing current impressed thereon by the operation of the connector. The energization of tube I56 effects the operation ofthe ringing trip relay (not shown) in the connector to cause the disconnection of the ringing current source and the closing of the talking connection in usual manner. The tube I56 is thereupon deenergized so that the connector does not reverse the current to operate relay 2I4 of trunk circuit TCI. Relay I55 connects ground to conductor I59 to operate the motor start relay MS of the ringing circuit,

and connects ground to conductor 39't'o operate the reset coil 32 of voltmeter relay'30 if at this time relay 33 of the permanent signal alarm cir' ated, due to the existence of a large'enough num-' ber of permanent signal conditions, the 'tone transmitting circuit is traced from the lower winding of tone transformer LTZ, through conductor I58, condenser I38, front contact of relay I31, back contact of relay I45, front contact of relayI 55, conductor 11'and brush H of connector C2, thence to the calling operator. If relay I45 is operated or if the ringing machine has ceased to operate, no tonev is transmitted, thereby indicating a major alarm. If relays I45 and I31 are normal and relay I48 has operated due to a re lease alarm condition, the tone is supplied through condenser I49 and conductor I51 from the tone transformer LTI. ,If relays I45, I31 and I48 are normal and relay I28 is operated clue to the continued existence of one or more permanentsignal conditions for an interval of twenty minutes or more in a first selector or subscribers line circuit, the tone. is supplied through condenser I30 from the code I ringingconductor of condition then existing, all of relays I45, I31, I48 and I28 are normal and tone is supplied through condenser I29 from the code 2 ringing conductor of the ringing circuit RC. When the calling operator releases the connection, the switches C2 and ISI are restored to normal, relay I55 releases, and the trunk circuits are restored to normal as hereinbefore described.

What is claimed is:

1. In a telephone system, lines, subscribers stations connected to said lines, selector switches for use in connecting calling and called lines, means for connecting each calling line with an idle switch, control means at each calling station for controlling the selective operation of the connected switch, alarm apparatus including an alarm relay, and means for operating said relay when a predetermined number of said switches have been connected to calling lines for a predetermined interval of time without being selectively operated.

2. In a telephone system, subscribers lines, permanent signal lock-out relays one for each of said lines, means comprising subscriber controlled selectors for completing connections between calling and called lines, line finders adapted to connect calling lines with selectors, means effective upon connection of a calling line with a selector for measuring a predetermined interval of time, means comprising an impulse sender at each calling station and relay means in each of the associated selectors for selecting a desired group and for selecting an unguarded set of terminals in the selected group, means efiective at the end of the measured interval for releasing the line finders associated with selectors which were associated with calling lines at the beginning of said interval and which have failed to complete terminal selection during said measured interval and for causing the operation of the look-out relays of the lines connected to said selectors, alarm apparatus comprising an alarm relay, and means responsive to the simultaneous operation of a predetermined number of said lock-out relays for operating said alarm relay.

3. In a telephone system, subscribers lines, permanent signal lock-out relays, one for each of a number but not all of said lines, means including subscriber controlled selectors for completing connections between calling and called lines, means comprising line finders adapted to connect calling lines with selectors, means effective upon connection of a calling line with a selector for measuring a predetermined interval of time, means comprising an impulse sender at each calling station and relay means in each of the associated selectors for selecting a desired group and for selecting an unguarded set of terminals in the selected group, means effective at the end of a measured interval of time for releasing the line finders associated with selectors which were associated with calling lines at the beginning of said interval and which have failed to complete terminal selection during said measured interval and for causing the operation of the lock-out relays of the lines connected to said selectors and equipped with lock-out relays, alarm apparatus comprising an alarm relay, and means for operating said alarm relay, said lastmentioned means being operatively responsive to the simultaneous operation of a predetermined number of said lock-out relays, or to the simultaneous connection of said predetermined number of lines to selectors which have not completed terminal selection, or to the simultaneous operation of a number of said lock-out relays and connection of a number of lines to selectors which have not completed terminal selection, the total of both of said last-mentioned numbers being equal to or greater than said predetermined number.

4. In a telephone system, an unattended office, a master office, lines including a troublechecking line in said unattended office, trunks between said offices, means in said unattended office for connecting calling lines with called lines and with said trunks and for connecting calling trunks with called lines, means in said unattended OfflCe responsive to a permanent signal condition existing on a predetermined number of lines for originating a call over one of said trunks and for connecting a distinctive tone to said trunk to indicate the character of the call thereover, the last-mentioned means comprising a marginal relay, means effective upon operation of said relay for locking said relay, means in said attended oflice for answering said call and for calling said trouble-checking line, means responsive to completion of a connection with said line for releasing said relay, and means for connecting a distinctive tone indicative of the character of the trouble to said trouble-checking line in case said predetermined number of permanent signal conditions exist when said trouble-checking line is seized.

5. In a telephone system, an unattended dial office, a master ofiice comprising an operators position, and trunks between said dial ofiice and said position, said unattended ofiice comprising subscribers lines, means including subscriber controlled switches for establishing connections between calling lines and called lines or trunks, and means responsive to a permanent signal condition existing at one time on more than a predetermined number of lines for seizing one of said trunks on a trouble indicating call to said position.

6. In a telephone system, an unattended dial office, a master office comprising an operators position and trunks between said dial ofllce and said position, said unattended ofiice comprising subscribers lines, means including subscriber controlled switches for establishing connections between calling lines and called lines or trunks, means responsive to a permanent signal condition existing at one time on more than a predetermined number of said lines for seizing one of said trunks on a trouble indicating call to the master ofiice, a trouble indicating tone source, and means responsive to the answer of the trouble call at the master office for connecting said tone source to said trunk to indicate to the answering operator the character of the call.

7. In a telephone system, an unattended dial ofiice, a master office comprising an operators position, trunks between said dial office and said position, subscribers lines in said dial ofiice, means including subscriber controlled switches for establishing connections between calling lines and called lines or trunks, an alarm relay in said dial office, and means comprising a voltmeter type relay responsive to the existence at one time of a permanent signal condition on more than a predetermined number of said lines for operating said alarm relay.

8. In a telephone system, an unattended dial ofiice, a master office comprising an operators position, trunks between said dial Office and said position, subscribers lines in said dial ofiice, means including subscriber controlled switches to answer of said call at said position for connecting the trouble indicating tone source to said trunk.

9. In a telephone system, an unattended dial office, subscribers lines in said ofiice, a master ofiice comprising an operators position, trunks between said dial office and said position, means including subscriber controlled switches for establishing connections between calling lines and called lines or trunks, an alarm relay in said I dial ofiice, meanscomprising a voltmeter type relay responsive only to the existence at one time of a permanent signal condition on more than a predetermined number of said lines for operating said alarm relay, said voltmeter relay comprising means for holding said relay operated and a reset coil for restoring the contacts of said relay to normal, means controlled by said alarm relay for seizing an idle one of said trunks on a trouble indicating call to said position, a trouble tone source, means responsive to the answer of said trouble call at said position for connecting said trouble tone source to said trunk, a trouble-checking line in said dial oflice, means at said position for initiating a troublechecking call over one of said trunks and for controlling the operation of switches in said dial office to establish connection with said troublechecking line, a line relay for said troublechecking line responsive to connection of a trunk therewith, means including contacts of said relay for operating said reset coil to release the voltmeter relay, means for preventing the reoperation of said reset coil while said line relay remains operated, a tone source for producing a tone indicative of a permanent signal alarm condition, and means effective if said voltmeter relay immediately reoperates after its release due to the operation of its reset coil for connecting said permanent signal; tone source to said trunk.

10. In a telephone system, an unattended office comprising subscribers lines and a troublechecking line, an attended oflice, trunks between said ofiices, switching means including first selector switches in said unattended oifice for connecting calling lines with called lines or with an idle one of said trunks and for connecting a calling one of said trunks with a called line, means for connecting each calling line with an idle one of said first selector switches, control means at each calling station for controlling the selective operation of vthe connected switch,

means in said attended office for connecting with an idle one of said trunks and for controlling the operation of switches in the unattended offlee to connect with any desired one of said lines, and means responsive to seizure of said troublechecking line for transmitting a trouble tone over the connected trunk in case a predetermined number of first selector switches are then connected to calling lines and said first selector switches have been so connected for a predetermined interval of time without being selectively operated.

JAMES N. WALTERS. 

